It is desirable to interrogate multiple wireless tags by sending from an interrogating transmitter a code and having information transmitted by the tag in response. This is commonly accomplished by having the tag listen for an interrogation message and for it to respond with a unique serial number and/or other information.
Since only one tag can be read at a time, some prior art devices and apparatuses have improved this interrogation and response process by utilizing a ready-quiet protocol. In the case of a ready-quiet protocol, the tags, once placed in the quiet state, must either timeout or be touched by a talk command before they can participate in an inventory. Several talk commands can be issued before an inventory, but there is no guarantee that multipath will be favourable, the frequency right, or even that a specific tag is physically close enough to the reader at that point in time. Any tags that miss the command or commands to wake up at the beginning of the inventory process will be missed, which is undesirable.
The use of a time-out for a persistent quiet is a conceptually simple alternative, but the manufacture of a tag that has a tightly controlled persistence time is difficult. Also, for example, 10 seconds might be too short a time to inventory a large number of tags, and yet 10 seconds might be long enough to interfere with multiple readers tracking an item on a trajectory or catching a shoplifter in the act of destroying a tag or putting the item into a shielded bag and walking away with an item.